/usr/ is in squirrelmail-lockout 1.7-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/
/usr/share/squirrelmail/
/usr/share/squirrelmail/plugins/
/usr/share/squirrelmail/plugins/lockout/
/usr/share/squirrelmail/plugins/lockout/functions.php
/usr/share/squirrelmail/plugins/lockout/index.php
/usr/share/squirrelmail/plugins/lockout/data/
/usr/share/squirrelmail/plugins/lockout/data/index.php
/usr/share/squirrelmail/plugins/lockout/setup.php
/usr/share/squirrelmail/plugins/lockout/locked_out.php
/usr/share/doc/
/usr/share/doc/squirrelmail-lockout/
/usr/share/doc/squirrelmail-lockout/README
/usr/share/doc/squirrelmail-lockout/copyright
/usr/share/doc/squirrelmail-lockout/changelog.Debian.gz
/usr/share/squirrelmail/plugins/lockout/data/config.php
/usr/share/squirrelmail/plugins/lockout/data/lockout_table.php